Output circuits for microwave discharge devices



April 8,1969 I N. 'r. LAVOO 3,437,949

' VOUI'IIPUT CIRCUITS FOR MICROWAVE DISCHARGE DEVICES.

' I Filed April 29, 1966 [n vent'orv J Norman '7."L.dvoo,

Nis Attorney.

United States Patent 3,437,949 OUTPUT CIRCUITS FOR MICROWAVE DISCHARGE DEVICES Norman T. Lavoo, Latham N.Y., assignor to General Electric Company, a corporation of New York Filed Apr. 29, 1966, Ser. No. 546,274 Int. Cl. H03f 3/60, 3/68 US. Cl. 330-53 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to improved output circuits for microwave discharge devices, and particularly to multituned output circuits providing improved gainban-dwith product.

There has been a continuing need for higher performance of space charge discharge devices, particularly triodes, and the improved performance is particularly desirable with respect to power gain over a substantial operating bandwith at a reasonably high center operating frequency. Recent improvements in electric discharge devices resulting in high trans-conductance and relatively low output capacitance have suited them for broadband operation. The present invention relates particularly to improved multituned output circuits for use with such devices to more fully attain the full operating advantages made possible by these improved devices.

In accordance with the illustrated embodiment of my invention, a three-cavity output circuit is provided in which the three cavities are formed in a section of rectangular waveguide defined, respectively by irises extending across the waveguide, the size of the openings in the irises determining the degree of coupling between the cavities. The output terminals of the discharge device e.g. the grid and anode terminals, are coupled to the opposite sidewalls of a first cavity portion of the guide. The first cavity is coupled to an intermediate cavity which is, in turn, coupled to an output cavity and an output circuit, specifically in the form of a concentric line, is capacitively coupled to the third, or output, cavity. Tuners in the form of adjustable plugs are located near the longitudinal centers of both the second and third cavity portions and these are adjustable individually to tune these cavities. In addition, a tuning plug is provided at the iris between the second and third cavities to tune the circuit with respect to modes in which there are substantial voltages at the iris. The coupling between cavities is substantially determined by the irises and is, therefore, determinable independently of the tuning by the capacitive loading provided by the plugs. In addition, the tuning pug between the second and third cavities serves to adjust the coupling between these two cavities and to increase the coupling beyond that accomplished by widening the iris opening alone. Further features and advantages of the invention will become apparent from the following detailed description of the illustrated embodiment, reference being bad to the accompanying drawing, in which:

FIG. 1 is a plan view, partially broken away, of a preferred embodiment of my invention;

FIG. 2 is an elevational view in section of the embodiment of FIG. 1; and

" ice FIG. 3 is a plan view, partially broken away, of a modified embodiment of my invention.

Referring now to FIGS. 1 and 2 of the drawing, I have shown my invention embodied in a three cavity rectangular waveguide output circuit, designated generally by the numeral 10, for a triode type discharge device 11 of disc seal construction, and including mutually insulated and spaced electrode terminals 12, 13, 14 and 1S, electrically connected respectively with the anode, control grid, cathode, and heater of the device 11. The anode and grid terminals are electrically connected respectively With the opposed walls 16 and 17 of the rectangular waveguide providing the output circuit 10. The anode connection is made through a plurality of spring fingers 18 which are supported in capacitively coupled relation to the sidewall of the waveguide 16 but insulated therefrom as far as direct currents are concerned, by insulating washers -19, suitably secured to the waveguide by a retaining ring 20. Spring fingers 21 provide the direct electrical connection of the grid terminal 13 with the opposite sidewall 17 of the Waveguide.

The input circuit is provided by a concentric transmission line structure including an outer generally cylindrical conductor 22 supported from and connected, both electrically and mechanically, to the sidewall 17 of the output waveguide circuit, and an inner conductor 23, spaced and insulated with respect to the interior wall of the cylinder 22 by a hollow insulating cylinder 24, The outer conductor is provided with an outer end wall 22a. The inner conductor 23 is recessed, as shown at 25, to accommodate a heater terminal 26 connected to the inner conductor 27 of a direct current heating supply connector, and also conductively connected with the device heater terminal 15 by a conducting spring 28. The center conductor 29 of another insulating connector is connected to the inner conductor 23 of the input transmission line to apply a negative direct current voltage to the cathode of the device. The anode is operated at a positive direct current voltage with respect to the cathode voltage. The inner conductor 23 of the transmission line is connected to the cathode terminal by spring terminal 30 to provide both a direct current and high frequency connection with the cathode. As illustrated, the high frequency connection to the input circuit is provided by a concentric connector 32 having an insulated inner connector 33 connected to the central conductor 23 of the transmission line by conductor 34. A small tuning disc 35, supported from the end wall 22a of the transmission line by threaded support 36, permits tuning of the input circuit. This provides a concentric line one-half wave length input circuit foreshortened at each end and having good characteristics over a wide bandwidth, i.e. 3 db over 30 percent bandwidth.

The output circuit is divided into three coupled cavities, an input cavity 37, an intermediate cavity 38, and an output cavity 39. The boundary between cavities 37 and 38 is provided by an iris including opposed members 40 and 41 which are movably supported in the sidewall of the guide at an angle with respect to the longitudinal axis thereof to provide a coupling gap in close proximity to the discharge device 11 and between the input cavity 37 and intermediate cavity 38. As illustrated in the embodiment of FIGS. 1 and 2, the input cavity 37 is narrow in transverse dimension compared to cavities 38 and 39, and this facilitates tuning of the input cavity to the desired degree, permitting more space between the input cavity tuning plunger 42 and the discharge device 11. As illustrated, the iris formed by members 40 and 41 enters the cavity at essentially the junction between the cavity walls of reduced spacing and the wider spaced walls of the intermediate cavity 38. A similar coupling structure between cavities 38 and 39 is provided by opposed members 43 and 44. The end wall of the output cavity is also provided by an adjustable plunger 45. The coupling irises provided by opposed members 40, 41 and 43, 44, as well as plungers 42 and 45, are all shown as movea-ble for adjustment purposes in the illustrated embodiment. It will be understood that, in a production version of the improved circuit, these members, except possibly plunger 42, may be fixed once the optimum dimensions and coupling for the circuit for a tube of given characteristics have been established. In accordance with an important feature of the present invention, provision is made for tuning cavities 38 and 39 independently of the coupling between the cavities which is determined by the position of the irisdefining members 40, 41 and 43, 44. As illustrated, a cylindrical threaded plug 46 extends into the intermediate cavity 38 at a high transverse electric field region thereof, i.e., near the longitudinal center thereof, and is adjustable with respect to the spacing between the end thereof and the opposite sidewall of the waveguide to provide capacitive loading of the cavity. In a similar manner, a tuning plug 47 is provided near the longitudinal center region of the output cavity 39. A concentric type output circuit is provided by a concentric type connector 48, also located in the central portion of the output cavity 39 and the central conductor of which terminates in a disc 49. The coupling with the cavity is adjusted by means of a suitable adjustable plug 50 having the end thereof located in opposed relation with the disc 49 and adjustable to adjust the output coupling. As illustrated, the output coupling is preferably in the same longitudinal position as the tuning member 47. In the operation of the three cavity device, there are standing waves of diiferent wave lengths present. In one mode, each cavity is a half wave length long with a voltage maximum near the longitudinal center thereof and a voltage minimum at the ends thereof. In a second mode, the three cavities are one wave length long in total length, so that there is a substantial voltage at the iris between the second and third cavities 38 and 39. In the third mode, the entire waveguide section is a half wave length long, in which case, also, there is a substantial voltage component at the iris between cavities 38 and 39. The provision of a capacitive loading or tuning plunger 51 at the iris between cavities 38 and 39 permits the extension of operation to wider bandwidths by increasing the coupling between the second and third cavities over that obtained by completely withdrawing iris members 43 and 44.

In the embodiment of the invention described above with an electric discharge device having a continuous plate current capability of 3 amperes and a 500 microsecond .07 duty factor pulsed plate current capability of 6.5 amperes, and an output capacitance of only 5.5 picofarads, the tube was successfully operated at the above pulsed duty cycle with a 20 db gain at a center frequency of 1324 megacycles and a bandwidth of 144 megacycles to the 1 db points. This is high gain operation at a high frequency over a wide bandwidth.

In the embodiment shown in FIG. 3, the cavities have been made of uniform width throughout, and the members 40 and 41, providing the iris between the input and intermediate cavities, extend from opposite sides of the waveguide. This construction works satisfactorily, but is less advantageous, particularly with respect to the tuning by the movable plunger 42, since the cavity is effectively shortened to a considerable extent by the capacity of the output electrode system of the discharge device.

4 While in the preferred embodiment of the invention illustrated three cavities have been employed, the invention in its broader aspects contemplates multiple coupled cavities, and specifically contemplates the use of two coupled cavities where the coupling is determined substantially independently of the tuning or loading.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A multiply tuned broad band amplifier circuit for coupling power from a pair of spaced electrodes of an electric discharge device to an output circuit comprising a rectangular waveguide having a pair of side walls, means comprising a plurality of pairs of wall members extending from said side walls into said waveguide for establishing a plurality of adjacent and electromagnetically coupled resonant regions along the length of said guide and each having an electrical length of substantially onehalf wave length at the resonant frequency, means coupling the output electrodes of an electric discharge device to the opposite walls of said guide at one of said regions, an output circuit coupled to a second of said regions, the respective members of each of said pairs of wall members being movable to determine the coupling between adjacent regions, and means for tuning said second region individually and independently of said coupling determining means enhance the bandwidth of operation of said amplifier circuit.

2. The combination of claim 1 wherein said first region is narrower than the remaining regions and the pair of wall members between the first resonant region and the second resonant region extend at an acute angle with respect to the longitudinal axis of the waveguide.

3. The combination of claim 2 wherein there are three resonant regions and a capacitive tuning member is located at substantially the longitudinal center of the second and thirdresonant regions.

4. The combination of claim 3 wherein a capacitive tuning member is located at the boundary between the second and third regions.

5. A triple tuned broad band amplifier circuit for coupling power from a pair of spaced electrodes of an electric discharge device from an output circuit com prising a rectangular waveguide, means establishing three adjacent and electromagnetically coupled resonant regions along the length of said guide, means coupling the output electrode of an electric discharge device to the opposite walls of said guide at one of said regions, an output circuit coupled to a second of said regions which is not adjacent said one of said regions, means comprising movable opposed wall members for independently determining the coupling between adjacent resonant regions, and means for individually tuning the second of said regions and the region adjacent thereto to enhance the bandwidth of high gain operation of said amplifier circuit.

6. The combination of claim 5 in which a tuning member is provided in the region of the coupling between said second and third resonant regions.

References Cited UNITED STATES PATENTS NATHAN KAUFMAN, Primary Examiner. 

